Mesenchymal stem cells give rise to the progenitors of many differentiated phenotypes including osteocytes, chrondocytes, myocytes, adipocytes, fibroblasts, and marrow stromal cells. Certain mesenchymal progenitor cells are capable of self-renewal and undergo expansion in the presence of transforming growth factor .beta.1 (TGF.beta.1), a pleotropic cytokine with autocrine and paracrine functions.
Transforming growth factor .beta.1 (TGF.beta.1), a 25 KDa peptide found abundantly in platelets and bone, released in response to tissue injury, is becoming an increasingly important tool for immunomodulation, wound healing, and tissue repair. TGF.beta. is also a chemoattractant for cells of mesenchymal origin, and as such, recruits fibroblasts to the site of injury, stimulates angiogenesis and de novo synthesis of extracellular matrix proteins in concert with the up-regulation of inhibitors of matrix degradation. See Roberts A. B., Sporn M. B.: The Transforming Growth Factor-.beta.s, pp. 420-472 (1990). TGF.beta.1 and TGF.beta.2 are potent immunoregulatory agents, suppressing the proliferation and function of T and B lymphocytes in vitro (Id.) and in vivo (See Wrann M, et al., "T Cell Suppressor Factor from Human Glioblastoma Cells Is a 12.5 KD Protein Closely Relating to Transforming Growth Factor-beta," EMP. J. 6:1633-36 (1987)). Hence, TGF.beta. appears to play a crucial role in clinically relevant disorders of immune surveillance, tissue regeneration, and repair. Moreover, repair after tissue injury such as burns, myocardial infarction, cerebral ischemia and trauma, as well as surgical wound healing, may be accelerated by a single systemic infusion or local application of this peptide growth factor. See Beck S. L., et al., "TGF-.beta.1 Induces Bone Closure of Skull Defects," J. Bone Mineral Res. 6(1991). The therapeutic effects of TGF.beta. administration may be augmented and/or prolonged by its pronounced autocrine and paracrine functions.
U.S. Pat. No. 5,486,359 (Caplan et al.) is directed to isolated human mesenchymal stem cells, and a method for their isolation, purification, and culturing. Caplan et al. also describe methods for characterizing and using the purified mesenchymal stem cells for research diagnostic and therapeutic purposes.
Heretofore, TGF.beta.1 has not been demonstrated to function as a survival factor, as opposed to a growth (proliferation) factor.